1. Field of the Invention
The present invention relates to a method to determine the error of orientational adjustment of the radiating face of an electronic scanning array antenna.
A brief description shall be given first of all of the working of an antenna of this kind. It constituted by a multitude of radiating elements, of the dipole type for example, generally positioned at the nodes of a regularly arranged (rectangular, triangular or more generally bi-periodic) plane mesh structure. An electronically controlled phase-shifter device is associated with each of these radiating elements. The value of the phase shift applied to a given element is a function of the desired direction of aim of the beam and of the position of this element in the array, in such a way that the values contributed to the radiation of the antenna by the various radiating elements get added together in phase in the chosen direction. The said position of the element is specified in a reference system (ox, oy) related to the radiating face of the antenna. The point of origin o is chosen generally at the center of symmetry of the array. The directions of ox and oy are those of the axes of symmetry of the mesh structure of the array. This reference system take the physical form, for example, of lines etched on the structure of the antenna. But it may also be purely virtual without being concretely represented in any way.
The state of each of the phase-shifters, namely the phase shift that each phase-shifter gives to the signal that goes through it, is controlled by a specialized computer called a "beam steering unit". The beam steering unit for its part receives its commands from the central computer of the radar in the form, inter alia, of two direction cosines, u and v, defining the desired direction of aim in the reference system (ox, oy), whether physically represented or not, related to the radiating face of the antenna. It may be recalled that u and v represent the components, in the reference system considered, of the projection, on the plane of the radiating face of the antenna, of the unit vector pointed in the requested direction of aim.
Independently of the existence or non-existence of the reference system (ox, oy), there always exists a physically represented reference system (IX, IY, IZ) attached to the structure of the antenna, generally located outside the radiating part, in which there are performed the optical aiming operations that are indispensable to the following operations:
firstly, aligning the entire aerial (radiating surface, rotation mechanism, support platform or turret, etc.) with respect to the absolute ground reference in which the radar is operating, PA1 secondly, measuring the precision of aim of the antenna during the qualification of this antenna as an instrument of angular measurement of radar targets. The inevitable defects of construction mean that this physically represented reference is not exactly parallel, as would be desirable, to the reference system (ox, oy) (made complete by the axis oz perpendicular to ox and oy). PA1 a rotation, which may be called a "defect of tilt" about the axis IX deemed to be horizontal, with a value .delta.x; PA1 a rotation about the axis IY, deemed to be vertical, with a value .delta..beta.; PA1 a rotation called a "rolling defect" about the axis oz, with a value .epsilon..gamma.;
2. Description of the Prior Art
The problem that arises then is that of precisely determining the orientation of the radiating face of the antenna with respect to the reference system (IX, IY, IZ). This orientation is defined for example by the values of the three elementary rotations:
Hitherto, the problem was resolved in the factory, before the installation of the aerial on the test site with a view to its qualification. This qualification comprised measurements of radiation patterns, gain, aiming precision, etc. This factory operation enabled the implementation, in weatherproof conditions, of the methods of standard metrology using systems of optical sighting and targeting by means of laser devices.
The main drawback of the usual method is that it calls for the antenna to be immobilized in the factory for a period of time that may cause problems with respect to increasingly heavy constraints in terms of time limits and therefore costs.